gprofng: pass gprofng location to gp-display-gui

gprofng GUI can be installed to the other directory.
In this case, $PATH is used to find gp-display-gui from gprofng
and option --gprofngdir is passed to gp-display-gui.

gprofng/ChangeLog
2023-08-09  Vladimir Mezentsev  <vladimir.mezentsev@oracle.com>

	* src/gprofng.cc (Gprofng::exec_cmd): Add option --gprofngdir.